The present invention relates generally to sound muffling devices and more particularly involves apparatus for use in the exhaust systems of internal combustion engines and in other sound muffling requirements such as in air compressors.
Conventional muffler devices utilized in automotive exhaust systems and on industrial engines mainly comprise two types of systems, a straight-flow system and a tortured-flow system. The straight-flow system generally uses a straight tubular flow member having perforated tubular walls around which is located a concentric outer shell packed with a sound-absorbment material such as steel wool or fiberglass. The system functions by absorbing the harsh peaks of sound through the perforations and into the packing material. Whereas the straight-flow system offers low flow restriction, it suffers from the disadvantages of being unable to effectively muffle the broad spectrum of exhaust noise, especially in automotive exhaust systems, and of containing numerous dead air spaces which trap moisture and accelerate corrosion. In fact, the straight-through muffler system has been banned by many municipal governments for use on automobiles because of its inability to muffle engine exhaust noise properly.
The second type of general muffler system involves the tortured-flow muffler currently in use in most automotive systems. This device utilizes a series of tubes, usually three or more, placed in an oval shell and containing several baffles. The tubes and baffles force the exhaust to make one or more 180.degree. turns while passing through the muffler, thereby reducing the noise level of the exhaust. Whereas the tortured-flow muffler is fairly effective at reducing exhaust noise, it suffers from the disadvantage of presenting a large amount of back pressure to the exhaust flow, thereby reducing the efficiency of the engine to which it is attached.
For example, the patent to Hilldring, U.S. Pat. No. 1,556,934 discloses a heavy-duty muffler comprising a very complex structure utilizing three varying sizes of internal concentric shells 11, 12, and 13 in conjunction with an outer shell 5 and three internal vertical baffle members 7, 8, and 9. The exhaust flow through the Hilldring muffler must follow a very tortuous path beginning in the inlet tube end and encountering the abrupt change at baffle member 7 which forces the gas to make a sharp right turn to flow through louvered ports at the outer periphery of baffle 7. The exhaust must then make another radical turn because of the action of baffle 8 to flow through perforations in inner shell 11. The flow must then make another 180.degree. turn, passing through the perforation of inner shell 12 into the annular area between baffle plates 8 and 9. The exhaust flow must then make another sharp 180.degree. turn through vents 9A and ports 13A in inner shell member 13 whereupon the exhaust flows around a sharp bend and out the outlet tube P. The Hilldring patent suffers many disadvantages including the fact that the tortuous flow path into which the exhaust flow is forced introduces a very high back pressure into the exhaust system, and the very large number of internal baffles and concentric shells create many dead air spaces, which in turn trap moisture and condensation as well as corrosive combustion products such as sulfides and other acids. This in turn causes a rapid deterioration of the muffler through the process of corrosion. The high back-pressure created in the Hilldring muffler greatly reduces the efficiency of the engine or compressor to which the muffler is attached and thereby increases the expense of operating with the Hilldring muffler in the system. Also, because of the very complex internal structure of the Hilldring muffler, including three different sized concentric tubular shells and various number of perpendicular baffles having 90.degree. bends, the Hilldring muffler is extremely expensive to manufacture and must be done on several different machines because of the large variation in structural elements internally. Also the welded and bolted construction of the Hilldring muffler further increases the expense and time required to manufacture it.
U.S. Pat. No. 1,761,971 to L. V. Cram discloses a muffler which utilizes a series of four internal baffles with restrictive flow paths formed through each baffle. The flow paths through each baffle are arranged to establish a swirling motion, but each succeeding baffle is arranged to swirl the gases in a different portion thereof. For example, in FIG. 3 the flow ports 6 extend near the outer circumference of baffle 2, whereas in FIG. 4 flow baffle 3 has the ports near the center thereof. The large number of baffles and the various locations of the flow ports therethrough likewise result in changing the flow direction of the exhaust gases a large number of times, plus the introduction of numerous zig-zags, swirls, and other motions in the flow gases. Also, the Cram muffler establishes a large number of dead air spaces such as, for example, around the edges of baffle 3 where there are no flow ports, which spaces serve to introduce corrosion traps for moisture in the muffler. Also the Cram muffler, by using a large number of baffles, i.e. four, serves to introduce a high back-pressure into the exhaust system.
The patent to Wilman, U.S. Pat. No. 2,808,896, discloses a muffler having a very complex, high-restriction system utilizing a single length gas flow path. The system does not take advantage of natural rotational forces. It consists of a single, extended exhaust tube having a concentric perforated inner shell through which the exhaust flows in a straight non-swirling motion through the system. The annular area between the perforated tube and the outer shell is packed with a sound absorbing material. No mechanical or rotational forces are introduced into the gas flow path. It is obvious from examining the Wilman patent that it contains a large number of corrosion traps whereby moisture is trapped and corrosion of the muffler is initiated.
The patent to Lentz, U.S. Pat. No. 3,479,145, discloses a catalytic converter which utilizes a very tortured flow path consisting of a series of three concentric shells with a large number of baffles located in each of the shells, and with flow ports formed through the walls of the various shells. The exhaust must travel a very tortuous path between the inlet and outlet of the Lentz device. The Lentz converter does not utilize varied flow lengths for the exhaust gases nor does it utilize swirl or natural rotational forces.
The Hutchins patent, U.S. Pat. No. 3,374,857, discloses a muffler which also serves as a separator for separating solid particles from exhaust gas. The muffler utilizes only a single length gas flow path and establishes large dead-air spaces. The Hutchins muffler is particularly susceptible to corrosion in the area behind the conical baffle 60, wherein condensation and acids will be trapped resutling in rapid failure caused by corrosion.
The patent to Irvin, U.S. Pat. No. 3,970,167, discloses a "hat box" shaped muffler having a centrally located outlet tube and a tangentially located inlet tube. The structure of the Irvin muffler is radically different from that of any other muffler due to its tangential inlet and central outlet locations. Because of this radical configuration the muffler is particularly unsuitable for location under a modern automobile due to the narrow space restrictions thereunder. Also, the Irvin muffler does not utilize variable flow lengths for the exhaust gases and contains many dead spaces and condensation traps which subject the muffler to rapid deterioration arising from corrosion.
Each of the above-mentioned prior art muffling devices suffers from various setbacks and disadvantages, including those of high back pressure, numerous dead air spaces, and single length flow paths. The present invention overcomes these disadvantages by providing a low-restriction, efficient muffling capacity sound muffler which utilizes natural rotational forces and continuously varied flow-port distances to provide a broad range of muffling ability without creating unnecessary engine power losses from back pressure buildup.